"Over two million people in Darfur are almost completely dependant on external assistance," Paul Smith-Lomas, Oxfam's regional director for East Africa, based in Nairobi, said in a statement.
"Most of the displaced people still do not feel safe enough to return home," he said.
"If they miss this year's planting season, the next harvest won't be until October 2006. An end to the fighting is urgently needed so people can begin to rebuild their lives."
Oxfam's grim warning came four days after the African Union decided to more than double the strength of its peace monitoring mission in Darfur to 7,731 personnel within five months.
For its part, Sundan said Saturday it has withdrawn its troops from four positions in Darfur, conceding to demands made by the African Union at abortive peace talks with rebels last November.
As many as 300,000 people have died since the Sudanese government unleashed Arab militias in a scorched earth campaign against Darfur's ethnic minorities following the launch of a rebel uprising two years ago.
Some two million others have fled their homes.
Oxfam said it was sending two planeloads of vital aid supplies to Darfur and another two to neighbouring Chad, where it said refugees in overcrowded camps face water shortages and disease.
"Over two million people in Darfur are almost completely dependant on external assistance," Smith-Lomas said. "Aid workers are doing all they can to help, but it simply isn't enough."
One of the Oxfam flights was to set off Monday for El Fasher in North Darfur with 34 tons of water and sanitation equipment to provide drinking water to more than 200,000 refugees.